[Insight-users] about gaussian filter

[Kevin H. Hobbs]

On Sun, 2006-03-12 at 19:34 -0800, liu jianfei wrote:
> hi
> 
>    I used itkrecussivegaussiangradientmagnitude to compute the
> magnitude of a 3D volume. I tried to set the deviation as 5, 10, and
> 20. I found that the magnitude of the image border was very large even
> it's the background voxel. Since the image is first convolved with the
> gaussian filter, can someone tell me how many voxels are used to
> integrate the convolution. As far as I know, it's usually controlled
> by the decay of the gaussian function, for example, it could be one
> sigma (deviation), two, etc. Can someone tell me what's the time of
> sigma? Thanks
> 
> 
>    have a nice day!

The standard deviations of the itk Gaussian functions are measured in
real world coordinates not in pixels.

I bet the image was padded with 0s and that the edges of the image were
not 0.  This would give a 'large' gradient magnitude.  Is your image
background white?

Is this the filter you are using?

http://www.itk.org/Doxygen/html/classitk_1_1GradientMagnitudeRecursiveGaussianImageFilter.html
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